Well you see, it's a short form for "gay ape", used to make fun of the people who would say "Booyah" (cuz thats pretty gay, and it sounds like a retarded ape).
When you beat someone in a street race so bad, you have virtually violated them. Lots of fan boys use the term Gap, but that's because their civics aren't very fast and all they ever do is "Gap" the other car. When you drive a real car, you can beat someone so badly, you have Gaped them. Left them violated, didn't even give them the courtesy of using lube.